In order to protect the passenger in the case where the vehicle is under emergency or comes into collision, the side airbag device including an airbag has been used. The side airbag device is mounted on a side section of the seat. The airbag inflates and deploys in a narrow space between the passenger and a sidewall (e.g., a door trim) of the vehicle, to thereby receive the passenger. Therefore, when the deployment speed of the airbag is slow, the door trim might hit the passenger. Furthermore, by contact of the airbag in the process of deployment with the passenger, accurate deployment of the airbag might be prevented.
The contact of the airbag with the passenger can be suppressed by deploying the airbag to the sidewall. However, in this case, the airbag is rubbed against the sidewall, thus deployment of the airbag might be slower. Furthermore, the airbag might also fail to deploy accurately. Therefore, from the viewpoint of secure protection of the passenger, the side airbag device is required to be accurately and quickly deployed. In contrast to this, there is conventionally known a side airbag device in which a part of the airbag is obliquely folded back to thereby speed up deployment of the airbag (see Patent Literature 1).
However, in such a conventional side airbag device, the airbag is continuously folded in half in the same direction, or alternately folded to thereby be folded in a bellows-like shape. Since such a folded airbag is unfolded swiftly, the airbag deploys quickly. However, since it is hard to regulate the deployment direction of the airbag, the deployment direction of the airbag might vary. Furthermore, some conventional side airbag devices have an airbag wound up in a roll-like shape in the same direction, and with such an airbag wound up in a roll-like shape, the deployment direction of the airbag can be regulated. However, it takes a long time to unwind the roll, and thus the deployment speed of the airbag might be slower. Therefore, it is difficult to achieve accurate and quick deployment of the airbag by using the conventional side airbag devices.